Progress and application of fresh-keeping technolo

Progress and application of fruit preservation technology (II)

2 2. Respiratory function

2 2.1 basic concept of respiration

impact strength can reach 45.7kj/m2

1 The picked fruits can also be used with 1-color wires. It does not mean the end of life, but another journey on the road of life. They are still breathing: Fruits absorb oxygen from the external storage environment, and oxidize and decompose their own organic substances, such as carbohydrates, proteins, organic acids] under the action of multiple enzymes after removing external forces. In particular, carbohydrates decompose into energy and water to maintain life activities and release carbon dioxide when oxygen is sufficient. If glucose C6H12O6 is used to represent carbohydrates in fruits, then respiration can be simply expressed by the following formula:

ch12o6 + 6o2 - 6CO2 + 6H2O + 674 kcal

the whole process of respiration is a series of enzymatic oxidation-reduction reactions, and part of the released energy is supplied to the fruits themselves for metabolism, To maintain the energy required for life activities; Another part of the form of instrumental heat is emitted from the fruit. This kind of heat energy emitted to the surrounding environment of the fruit is called respiratory heat. Often, when fruits are piled up, it is found that there is heat and temperature rise in the pile, which leads to decay. Especially in the case of poor ventilation

2. The respiration process of fruits can be divided into two parts: one is the process without the participation of molecular oxygen, which is anaerobic respiration or fermentation; The other part is a process in which molecular oxygen must participate, which is called aerobic respiration. Anaerobic respiration can be simply expressed as follows: c6h12o6--2c2h5oh+2co2+28 kcal

obviously, the energy output value produced by anaerobic respiration is also large enough, which is 1/24 of aerobic respiration. In order to maintain life activities under anaerobic conditions, fruits must consume stored nutrients to produce enough energy, and produce a large amount of ethylene and hexanol at the same time. The massive accumulation of these substances will inevitably poison the fruit tissue and degrade its quality. Therefore, long-term anaerobic respiration is harmful to the fruit storage room

2. 2.2 effect of storage environment on fruit respiration

1 Temperature: closely related to respiration. Generally, increasing temperature increases respiratory intensity. However, when the temperature is greater than 35 ℃, the enzyme activity of the catalytic reaction will be reduced and denatured when the temperature is increased. On the contrary, cooling can reduce respiratory intensity and prolong storage life. However, the lower the temperature, the better. Different varieties of fruits have different adaptability to low temperature, but there is a limit. Too high or too low temperature will affect the normal life activities of fruits, and even hinder the normal post ripening process, causing physiological damage and death. Therefore, the appropriate temperature should be selected for storage. At the same time, the storage temperature should be kept stable, because the fluctuation of temperature will accelerate respiration and increase material consumption, which is not conducive to extending the storage life

2. Gas composition

(1) oxygen: oxygen in the environment will affect the respiratory intensity and respiratory pathway of fruits. Generally, the respiration of fruits decreases with the decrease of oxygen concentration in the environment, and the climacteric period of respiration is delayed, and the storage life is prolonged. When the oxygen concentration is less than 2%, it is mainly hypoxic respiration, which is easy to cause injury. (2) Carbon dioxide: directly affects the respiration of fruits and affects their storage life. When the concentration of carbon dioxide is too high, respiration is inhibited, and anaerobic respiration is carried out continuously, so that there is too much hexanol and hexanal accumulated in the fruit, which will poison the fruit, cause physiological damage, and lead to the death of the fruit. This kind of damage is faster and more serious than the physiological damage caused by hypoxia. Appropriate carbon dioxide concentration can not only inhibit respiration and reduce the loss of nutrients, but also inhibit the activities of chlorophyll hydrolase and pectin hydrolase, which has a significant effect on keeping fruits green, hard and fresh. At the same time, carbon dioxide also inhibits the catalytic effect of ethylene, which plays a good role in delaying the ripening and aging of fruits

(3) ethylene: it is a gaseous plant hormone, which can increase respiratory intensity and catalyze premature fruit aging

3. Mechanical injury: crushing, collision, pricking and other injuries will increase the respiratory intensity of the fruit, thus shortening the storage life and accelerating the ripening and aging of the injured fruit. It is easily infected by pathogenic microorganisms and rots

4. Humidity: it plays a decisive role in the evaporation of fruits

2. 3 evaporation

the water content in the body of the harvested fruit is reduced due to evaporation, and the activity trend of the enzyme is towards hydrolysis, so as to consume the nutrients in the fruit and reduce its storage resistance. At the same time, the commodity value is lost due to water loss and withering